The invention relates to a method for monitoring the operation of a component, a control system for monitoring the operation of a component, as well as to a vehicle system comprising such control system. The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as trains, passenger cars, etc, as well as in other applications such as marine engines, constructional equipment, aviation industry, etc.
Various mechanical components are subject to loads causing material stress in the components. If the material stress is applied during a certain time it will eventually cause material fatigue in the components whereby the mechanical and/or physical properties of the components will eventually degrade and cause damage or failure of the components.
In vehicles a number of components are subject to conditions exposing them for loads and material stress during operation. One such component is e.g. the turbine wheel of a turbo charger. When the turbine rotates the changes in centrifugal forces will induce expansion or contraction of the turbine wheel in a cyclic manner thus leading to material fatigue in the long run.
A number of techniques for determining the material fatigue have been proposed. One such technique is the so called Rainflow algorithm, which algorithm is designed to calculate the peaks and valleys of a set of data samples representing e.g. the rotational speed of a component. For each cycle, i.e. each subset of data samples extending between two peaks or two valleys the amplitude is stored in a matrix, which matrix is evaluated in order to determine the degree of material fatigue of the component.
One method implementing the Rainflow algorithm on-board is mentioned in US2010/0174576, describing how structural status within vehicle systems may be monitored. A fixed size memory buffer is used for collecting streamed data from system sensors, and peak cycles are used for determining the material fatigue. During real time monitoring the fixed size buffer will eventually be filled with data, thus requiring either i) disregarding new data, or ii) throwing away old data. For performing a reliable monitoring it is required that all data is used. On the other hand the available computing power and memory do not allow for unlimited storage and processing capacity. Hence, there is a need for an improved method for monitoring the operation of a component using fixed size memories without disregarding any data.
It is desirable to provide a method for monitoring the operation of a component, which method overcomes the above mentioned drawbacks of prior art methods.
By the provision of a method which when the buffer is full performs the steps of i) deleting the information relating to the oldest local extrema from the fixed-size buffer; ii) calculating a pseudo cycle formed between two endpoints of which one endpoint is represented by the deleted oldest local extrema; and iii) storing information related to the calculated pseudo cycle in the memory, no important data will be disregarded for determining the fatigue of the component. Hence, a more comprehensive and more reliable monitoring may be achieved.
According to one embodiment, the fixed-size buffer is a ring buffer. Hence, there is no need for a fixed start position in the buffer.
According to one embodiment, the step of storing information relating to each local extremum in a respective position of the buffer is performed such that the information is stored in the same sequential order as the associated local extrema appear in the data sample stream. This is advantageous in that the method may be performed in real time whereby the buffer is continuously updated as the data sample stream is provided.
According to one embodiment, the step of receiving a stream of data samples is performed continuously during operation of the component. Hence, in a vehicle application the method may be performed during the complete running time of the vehicle thus improving the accuracy of the method.
According to an embodiment, the step of storing information related to said cycle in a memory is performed such that said information comprises the amplitudes of the local maxima and the local minima, respectively. This is advantageous in that the method may implement available methods for determining the degree of material fatigue, such as Miner's rule requiring cycle amplitude as input.
According to an embodiment, the step of deleting the local extrema corresponding to at least one of the endpoints of the cycle from the buffer further comprises the step of shifting the respective positions of the remaining information in the buffer such that the remaining information is stored in a consecutive order.
According to an embodiment, the method may further comprise the step of classifying the information related to the cycles in predetermined intervals, wherein each interval is associated with the minimum amplitude and the maximum amplitude of the cycle. This is advantageous in that large amplitude cycles may be associated with a greater impact on material fatigue than small amplitude cycles.
According to an embodiment, the step of storing information related to the cycle in a memory is performed such that the information is stored in a position of the memory being assigned to the interval. The memory may thus be configured as a matrix, wherein each position of the matrix is associated with a specific interval.
According to an embodiment, the step of calculating a pseudo cycle is performed such that the calculated pseudo cycle is classified in an interval being associated with the most probable cycle. In another embodiment, the step of calculating a pseudo cycle is performed such that the calculated pseudo cycle equals a cycle having the highest maximum amplitude and the lowest minimum amplitude. Hence, the method may be performed differently depending on the particular components being monitored.
According to an embodiment, the method may further comprise the step of calculating a value from the information stored in the memory, which value represents a status of the component. The method is thus capable of providing a real time value of the degree of material fatigue of the particular component.
According to an embodiment, the step of calculating a value from the information stored in the memory is performed using Miner's rule.
According to an embodiment, the operation of the component represents the rotational speed of a turbine wheel in a vehicle, and wherein the status represents fatigue of the turbine wheel. This is advantageous in that the method is used for a critical component, which in case of damage affects the overall performance and engine characteristics of the vehicle.
According to an embodiment, the step of calculating a value from the information stored in the memory is repeated during operation of the component, and wherein the method further comprises the step of storing each value. The method may thus be performed onboard a vehicle in real time.
According to an embodiment, the method may further comprise the step of comparing the calculated value with a reference value, which reference value corresponds to component failure. The method is thus capable of not only providing a real time monitoring of the material fatigue of the component, but also to provide an output indicating the current operation of the component relative component failure.
According to an embodiment, the method may further comprise the step of extrapolating the stored values in order to predict maintenance of the component.
According to a second aspect, a computer program comprising program code means is provided for performing, the steps of the method according to the first aspect when said program is run on a computer.
According to a third aspect, a computer readable medium carrying a computer program comprising program code means is provided for performing the steps of the method according to the first aspect when said program product is run on a computer.
According to a fourth aspect, a control unit for monitoring the operation of a component is provided, the control unit being configured to perform the steps of the method according to the first aspect.
According to a fifth aspect, a control system for monitoring the operation of a component is provided.
According to sixth aspect, a vehicle system comprising a control system in accordance with the fifth aspect is provided.
In an embodiment, the vehicle system further comprises a turbine wheel, wherein the receiving unit is configured to receive a stream of data samples representing the actual rotational speed of the turbine wheel.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.